The present invention relates to a deflection unit for a CRT having a yoke ring mounted on and secured by means of adhesive to a deflection coil assembly comprising a support carrying a set of deflection coils. The invention relates also to a method of manufacturing a deflection unit for a CRT which method comprises the steps of mounting a yoke ring on a deflection coil assembly and securing the yoke ring to the deflection coil assembly by means of adhesive.
There is disclosed in EP-A-0 534 531 a deflection coil assembly and a method for its manufacture in which a preformed and shaped set of deflection coils, for example, a set of vertical, or field, deflection coils of the saddle-type, is secured on the outer surface of a hollow coil support of synthetic material by means of an ultrasonic welding technique through which portions of the support are softened by localised heating and urged towards the deflection coils such that the coils of the support become joined, and fixed, together. A set of horizontal, or line, deflection coils is secured to the inner surface of coil support in similar manner. After forming the coil assembly in this way, the yoke ring, which is flared and conforms generally to the outer surface shape of the assembly, is positioned over the outer surface of the assembly, with the wider, base, end of the flared yoke ring resting against a radially extending part of the coil assembly, and secured in position.
In a known method of securing the yoke ring to a coil assembly, a ring of epoxy resin is applied around the smaller diameter, neck, end of the yoke ring which bridges the gap locally between the radially-extending end face of the yoke ring and the coil assembly and secures the yoke ring to the assembly at that end while the wider end of the yoke ring is bonded to the radially extending part of the assembly, comprising a radial surface of the support supporting portions of the field coils, by applying separately a polyurethane resin at spaced locations around the periphery of the outer surface of the yoke ring at its base end which runs, through gravity, onto the radial part of the assembly to connect and bond the base end of the yoke ring to the assembly. In this way, the yoke ring is secured to the deflection coil assembly at both ends. Application of the epoxy and polyurethane resins to the neck and base of the yoke ring is automated. The epoxy resin and polyurethane resins are supplied from separate dispenser nozzles, the epoxy resin being applied to neck of the yoke ring while effecting relative displacement between the coil assembly, carrying the yoke ring, and the dispenser nozzle and the polyurethane resin being applied in a static process in which predetermined quantities of the resin are dispensed through separate outlets positioned around the yoke ring towards its base.